Abstract
In chronic inflammatory diseases such as obesity, tissue and cellular homeostasis are disrupted by persistent low-grade inflammation, where one of the most prominent pro-inflammatory cytokines that correlates with age and body mass index (BMI) is IL-6. All members of the IL-6 family of cytokines signal through their obligate co-receptor gp130, in whichsignaling tyrosines on the intracellular portion of gp130 activate multiple downstream pathways such as the canonical STAT and MAPK pathways. However, non-canonical gp130 pathways such as SRC family of kinases (SFKs) signaling have emerged as drivers of cellular stress response. Our recently published mutant mouse model carrying a constitutive inactivation of gp130-Y814 (F814 mice), which impairs SFK activation, exhibited an enhanced resolution of inflammatory responses and improved regenerative outcomes in both acute skin wound healing and post-traumatic osteoarthritis models. The current study was designed to explore whether the gp130-Y814 mutation reduces systemic chronic inflammation and multimorbidity in a high-fat diet (HFD)-induced model and to interrogate the possible downstream cellular mechanisms that are affected. In response to HFD, F814 mice showed significantly reduced systemic and tissue-specific inflammatory responses and protection from obesity-induced bone loss and osteoarthritis compared to wild type (WT) mice. After extensive characterization, the role of gp130-Y814 in monocytes/macrophages appeared to be dispensable, but we discovered that the F814 mutation blunts gp130 receptor internalization, p38/MAPK activation and the release of matrix metalloproteinases (MMPs) in chondrocytes. Finally, we showed that F814 chondrocytes had markedly reduced activation of the SFK-dependent GTPase dynamin 2 (Dyn2) in response to catabolic IL-6 cytokines. Introduction of a dominant-negative Dyn2 mutant into WT chondrocytes phenocopied the effects of the F814 mutation, resulting in attenuated p38/MAPK signaling and reduced MMP activation following stimulation with IL-6 cytokines. This study demonstrates, for the first time, that the Y814 residue is directly implicated in Dyn2-mediated internalization of the gp130 receptor, thereby modulating downstream signaling and contributing to pathological outcomes in chronic inflammatory and degenerative diseases in a cell type-specific manner.